Method for manufacturing fiber-reinforced parts utilizing stereolithography tooling

ABSTRACT

A method of manufacturing a three-dimensional fiber-reinforced part utilizing the single-tool method of stereolithography. The tool is fabricated by designing the tool on a computer-aided design system and curing successive layers of a fluid medium via a computer-controlled irradiation source to form the three-dimensional tool. The desired part is generated by applying layers of resin-wetted fabric to the tool, curing the fabric on the tool, removing the tool from the designed part and cleaning, trimming and inspecting the designed part.

TECHNICAL FIELD

The present invention relates to methods for manufacturingthree-dimensional parts, and more specifically to a method formanufacturing fiber-reinforced three-dimensional parts utilizingstereolithography tooling.

BACKGROUND OF THE INVENTION

The manufacture of fiber-reinforced three-dimensional parts is typicallyaccomplished by one of two methods: master tooling; or "contact lay-up."The master tooling method includes the fabrication of a solid patterntypically of wood or metal via a multi-step tooling process. This methodof tooling is not employed often due to th craftsmanship skills andexperience needed to work with a solid wood or metal pattern.

Generally, the contact lay-up method of tooling includes the steps of:(1) fabricating a tool; (2) applying resin-wetted layers of fibermaterial to the tool; (3) curing the fiber layers; (4) removing thetool; and (5) trimming and cleaning the part. The primary disadvantageof this method of tooling is the amount of time and expense incurred tofabricate the tool. Manufacture of a single three-dimensional part bythis method requires a minimum of three intermediate tools. If the partto be manufactured includes negative draft angles or other complexshaping requirements, more than three intermediate tools may berequired. Additionally, design changes are difficult to incorporate.Finally, human error, storage and maintenance requirements, andlabor-intensive in-processing severely limit this method.

Thus a need has arisen for a manufacturing method wherebyfiber-reinforced three-dimensional parts are created utilizing asingle-tool process, thereby minimizing material, time and laborresources while offering greater flexibility and accuracy.

SUMMARY OF THE INVENTION

The present invention overcomes the foregoing and other problemsassociated with the prior art by providing a manufacturing methodutilizing stereolithography for making fiber-reinforcedthree-dimensional parts.

The present invention is a method for the manufacture offiber-reinforced parts utilizing the single-tool fabrication step ofstereolithography. Stereolithography ("SLA") is a method for generatingthree-dimensional articles within a fluid medium (photopolymer) byselectively curing successive layers of the liquid medium through theuse of a computer-controlled irradiation source and a translationmechanism. SLA is known in the art and is currently utilized tofabricate engineering concept models and as patterns for sand andinvestment casting.

The method of the present invention includes the following steps: (1)fabricating a tool using SLA; (2) applying layers of resin-wetted fabricto the tool; (3) curing the fabric layers; (4) removing the tool aftercuring; and (5) cleaning and trimming the part.

The method of the present invention allows three-dimensionalfiber-reinforced parts to be generated simply, quickly and economically,even where such parts are complex in shape or require design variations.Since the part is designed with the aid of a computer, human errorduring the processing stages is virtually eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a flow chart representing the steps associated with th presentinvention for the manufacture of fiber-reinforced parts utilizingsingle-tool fabrication; and

FIG. 2 is a schematic diagram illustrating the fabrication of a singlepart using the single-tool manufacturing method of the presentinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 1, there is illustrated a flow chart representingthe steps associated with the present invention for the manufacture offiber-reinforced parts utilizing single-tool fabrication is shown.

First, a part is designed at step 10 on a computer-aided design system.This designed part is stored such that the part can be recalled and thenreused and/or modified to incorporate design changes for the part. Thedesigned part can also be recorded on paper media. Next, the part designis sliced into numerous imaginary cross-sections using stereolithography("SLA") software in step 12. Once the design has been divided intocross-sections, a computer-controlled irradiation source (e.g., a laser)within a stereolithography apparatus is passed over the surface of a vatof photopolymer in step 13. A photopolymer is a liquid medium whichresponds to exposure to an irradiation source by changing states from asubstantially liquid state to a substantially solid state. The computerguides the laser across the surface of the photopolymer according to thecross-sections of the part to be formed.

A the photopolymer is selectively cured into solid cross-sections of thepart to be formed, the newly solidified cross-sections are slightlylowered from the surface of the photopolymer so that the nextcross-section can be formed. This method of tooling avoids the multiplesteps necessary with the prior art methods of tooling and allows thepart to include complex shape requirements such as negative draftangles. The SLA tool is formed once all of the cross-sections have beencured by the irradiation source. The photopolymer used has the physicalcharacteristic of brittleness when in a solid state. This allows the SLAtool to be easily broken away during a later step in the method.

Once the SLA tool is cleaned in step 14, the surface of the tool isprepared with a sealant and parting agent in step 16. Then, in step 18,successive layers of a resin-wetted fiber material are applied to thesurface of the SLA tool. These layers of fiber are allowed to curebefore the SLA tool is broken away in step 20. The final part istrimmed, cleaned and inspected in steps 22 and 24.

In FIG. 2, there is shown a schematic of a single part, for example anairplane part, manufactured utilizing the single-tooling method of thepresent invention. The part 26 to be manufactured is first designed on acomputer-aided drafting system 28. A SLA system 30 then fabricates atool directly from the design. The SLA system 30 creates numerousimaginary cross-sections of the part 26 to be manufactured. Thecross-sections are formed from a vat 32 of a photopolymer 34 capable ofphysical state changes upon exposure to an irradiation source (e.g.,laser) 36. A photopolymer having the physical characteristic ofbrittleness upon curing is desirous so that the tool can be easilyremoved in a later step of the process. An example of such aphotopolymer is the CIBATOOL resin photopolymer, product numberSL-XB-5081-1, from Ciba-Geigy, Inc.

Within the SLA system 30, a computer-controlled optical scanning system(not shown) moves the laser across the surface of the photopolymer 34such that the photopolymer is cured according to the cross-sections ofthe part to be designed. As each successive cross-section is formed fromthe surface of the photopolymer 34, the cross-section is loweredslightly to allow the next cross-section to be formed from the vat 32 ofphotopolymer 34.

Once a SLA tool 38 is formed from the cross-sections of the part 26, thetool 38 is completely cured in a post curing apparatus (not shown). Oncecured, the tool 38 is prepared with a sealant and a parting agent. Thetool 38 is then covered with successive layers of a resin-wetted fibermaterial 40 and allowed to cure. An epoxy or polyester resin istypically used. The amount of fiber material 40 used is determined bythe structural requirements of the part 26.

Curing of the fiber material 40 is accomplished in approximately 12-24hours at room temperature, or in a much shorter period (approximately anhour) by placing the fiber-coated tool in an oven elevated to 150degrees Fahrenheit. After curing, the SLA tool 38 is shattered andremoved from the interior of the designed part 26. Once trimmed andcleaned, the finished part 42 is quality inspected and ready for use.

Although a preferred embodiment of the invention has been illustrated inthe accompanying drawings and described in the foregoing DetailedDescription, it will be understood that the invention is not limited tothe embodiment disclosed, but is capable of numerous rearrangements andmodifications of parts and elements without departing from the spirit ofthe invention.

We claim:
 1. A method for producing a fiber-reinforced part utilizingstereolithography tooling, comprising the steps of:designing a part on acomputer-aided design system; stereolithographically fabricating a toolfrom the designed part; applying fiber material to the tool; curing thefiber material applied to the tool; and removing the tool for finalfinishing of the designed part.
 2. The method of claim 1 wherein thestep of designing a part on a computer-aided design system includes thestep of creating multiple imaginary cross-sections of the part.
 3. Themethod of claim 1 wherein the step of stereolithographically fabricatinga tool from the designed part includes the step of passing anirradiation source over a liquid medium capable of selective physicalstate transformation upon exposure to the irradiation source.
 4. Themethod of claim 3 wherein the step of passing an irradiation source overa liquid medium includes the use of a photopolymer that changes from asubstantially liquid state to a substantially solid state upon exposureto the irradiation source.
 5. The method of claim 3 wherein the step ofpassing an irradiation source over a liquid medium includes the use of asubstantially liquid photopolymer having the physical property ofbrittleness when solidified.
 6. The method of claim wherein the step ofstereolithographically fabricating a tool from the designed partincludes the step of preparing the tool for the application of a fibermaterial.
 7. The method of claim 1 wherein the step of applying fibermaterial to the tool includes the steps of applying multiple layers of aresin-wetted fiber material.
 8. The method of claim 1 further includingthe step of trimming and cleaning the resulting part.
 9. A method forproducing a fiber-reinforced part utilizing stereolithography tooling,comprising the steps of:designing a part on a computer-aided designsystem; creating multiple imaginary cross-sections of the part;stereolithographically fabricating a tool from the designed part bypassing an irradiation source over a photopolymer responsive uponexposure to said irradiation source by changing from a substantiallyliquid state to a substantially solid state; said photopolymer havingthe physical characteristic of brittleness when solidified; preparingthe tool for application of a resin-wetted fiber material; applyingmultiple layers of the resin-wetted fiber material to the tool; curingthe fiber material applied to the tool; and removing the tool for finalfinishing of the designed part.
 10. The method of claim 9 wherein anepoxy or polyester resin is used to wet the fiber material.